Method of producing magnetic materials



I No Drawing.

Patented May 17, 1932- UNITED STATES PATENT OFFICE CHARLES PHILIP DEATH, OF LA QRANGE, AND HERBERT MARTIN EDWARD HEINICIKE, OF ELGIN, ILLINOIS, ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPORATED. OF NEW YORK, N. Y., A CORPORATION OF NEW YORK METHOD OF PRODUCING MAGNETIC MATERIALS.

v make it highly desirable in electrical signaling apparatus, especially in cores for loading coils for telephone circuits.

The magnetic material produced in accordance with the invention is of particular advantage in the )roduction of magnet cores of the so-called ust type in which a magnetic material is reduced to very finely divided particles, the particles treated to produce an insulating coating thereon and pressed into rings or cores. One method of utilizing the finely divided magnetic material to produce loading coil cores is described in United States Patent No. 1,669,643, granted May. 15, 1928, to J. W. Andrews and R. Gillis. However, the magnetic material is not limited in its use to the particular insulator disclosed in the foregoing application nor to any particular form of core, but may be put to any use within the scope of the appended claims.

In accordance with one embodiment, the present invention contemplates the production of brittle alloys of nickel and iron by partially oxidizing the constituent metals while in the molten state and working the metal in the solid state, while hot, to produce a fine crystalline structure. More specifically, the invention contemplates the production of brittle nickel iron alloys, generally known as permalloy in which the proportions of its constituents are more than 25% nickel and the remainder principally iron, one form which has proven satisfactory having a nickel content which is approximately 80% of thehwhole.

In thisembodiment the constituents are melted in the presence of oxygen and an Application filed October 29, 1927. Serial No. 229,790.

oxidizing substance, the molten material is boiled until it is oxidized, is poured into a mold and allowed to solidify. The solidified material is then rolled while hot to produce a fine crystalline structure at such a rate that the material reaches a temperature slightly above that at which it ceases to be malleable at about the same time that the final reduction of the material is efiected.

One method of oxidizing the metals constitutin r the alloy is .disclosed in United States 1 atent No. 1,669,649, ranted May 15, 1928, to C. P. Beath and H. E. Heinicke, but for the sake of completeness it will also be described in detail herein.

The method of producing the brittle, fine grained material in accordance with the invention consists in placing the required quantities of nickel and iron in a suitable furnace, preferably electrically heated, adding acalculated quantity of oxidized material of the same purity, and heating the material until it is molten under oxidizing conditions. Since, if virgin metal is used, it requires considerable time to obtain a melt which is oxidized to the right degree, oxidized material may be added to furnish additional oxygen to reduce the time consumed in completing the operation. Iron oxide in the form of iron ore may also be added to furnish oxygen within the bath. When the material has become molten it is oxidized by boiling for a length of time determined by the amount of oxidation desired and the type of furnace used. The degree of oxidation of the material depends upon the length of the melting period, the length of the boiling period, the amount of the surface of the melt exposed to the air, and the amount of oxygen present in the charged material, and the heating and boiling periods are governed by the various charges and the type of furnace used. After the molten material has been oxidized to the required degree, it is then poured into an ingot mold, and as soon as the material is solidified, the mold is removed and the ingot is allowed to cool.

Samples of the material are taken from various parts of the ingot for analysis and if the material is of the required composition it is placed in a furnace where it is heated to approximately 1325 C. at wh1ch temperature it may be easily rolled. In order to obtain a fine dust, the material should have a very fine crystalline structure which is obtained by successively passing the hot billets fromthe heating furnace, withouta subsequent reheating, through progressively reducing rolls at such a rate that the material passes through the final reducing roll at about the time that the material has cooled to a temperature slightly above that at which the material ceases to be malleable.

The working of the metal breaks down'the large grained, crystalline structure of the b1llet and produces a very fine gralned crystalline product which is extremely brittle. Since the final reduction in the size of the crystals is effected at a temperature which 15 only slightly above that at which the material ceases to be malleable, and since this temperature is not far removed from the temperature of recrystallization of the material, there is little opportunity for the crystals to grow in size after the final rolling operation and the resulting product has an extremely fine crystalline structure. This is ver desirable because in this material the racture takes place principally along the crystalline boundaries and consequently the smaller the size of the crystals the finer the dust which can be produced from the finished product. Should the material become cooled while passing through the rolls to a temperature slightly above that at which it ceases to be malleable before the final roll is reached, the rolling operation may be stopped and the material reheated to a temperature at which it becomes malleable and the rolling operation continued provided, however, that the final rolling operation is efiected as hereinbefore described at'a temperature slightly greater than that at which the material loses its plasticit Tlie material obtained by the above out-- lined operations is crushed in a jaw crusher, hammer mill, or any other suitable type of apparatus, after which the crushed material is rolled in a ball mill until it is reduced to a fine dust. The dust is sieved through a 120 mesh sieve and any residue is remelted and carried through the above operations to again reduce the material to a finely divided form.

By using an alloy of the proportions stated in the preceding paragraph and by following the foregoing method of procedure, a very fine grained crystalline product is obtained which is extremely brittle and which when reduced to a fine dust yields a large percentage of particles which are small enough to pass through what is commonly known as a 200 mesh sieve. When reduced to a finely divided form, the material is then in a form to be used for either continuous or lump loading of telephone circuits.

The finely divided magnetic material obtained by the above described methods is particularly adapted to be formed into rin s or cores for loading coils in any suitab e manner. In one method which has )roven satisfactory the finely divided particles are heated to a high temperature, are individually insulated by treating the particles in such a manner as to produce an insulating coating around each particle, the insulated material formed into rings or cores by theapplication of a high pressure, and the rings annealed to stabilize the insulator and to give the rings the desired magnetic properties. A plurality of rings thus formed are then stacked coaxially to form a core on which the usual toroidal winding is applied, the number of such rings used depending upon the existing electrical characteristics 0 the telephone circuit with which the loading coils are to be associated. Since, in order to have low losses in loading coil cores made of permalloy dust in the above described manner, it is desirable that all of the material pass through a 120 mesh sieve and a large percentage pass through a 200 mesh sieve, it is readily seen that the material produced according to this invention is especially adapted to be used in the production of such cores.

By the statement employed hereinbefore and in the annexed claims that the final rolling of the material is effected at a tempera ture slightly above that at which the material loses its malleability is meant that the material is rolled at a temperature slightly greater than the lowest temperature at which material reductions in the dimensions of the piece of material being worked upon may be produced by a rolling operation in which the piece remains intact.

What is claimed is 1. A method of producing magnetic materials, which consists in heating a ma netic material to temperature at which it becomes malleable, and working the material until it reaches a temperature slightly above that at which it ceases to be malleable.

2. A method of producing brittle magnetic materials, which consists in heating a piece of an iron nickel alloy to a temperature above that at which it becomes malleable, and progressively reducing the crosssectional dimensions of the piece until it reaches a temperature at which the alloy ceases to be malleable.

3. A method of making fine crystalline structures from brittle magnetic materials, which consists in heating the material to a temperature of approximately 1325 C., working the material until it reaches a temperature slightly above that at which it ceases to be malleable to produce a fine, crystalline structure.

4. A method of making fine crystalline structures from brittle oxygenous magnetic alloys composed of more than 25% nickel and the remainder principally iron, which consists in heating the alloy to a tem erature of approximately 1325 C. and rol ing the alloy until it reaches a temperature slightly above that at which it ceases to be malleable.

5. A method of preparing fine crystalline structures from a brittle alloy comprising parts of nickle and 20 parts of iron, which consists in heating the allo and rolling the allo while hot until it reac es a temperature slig itl above that at which it ceases to be mallea le.

6. A method of preparing brittle magnetic materials, which consists in heating a piece of a nickel-iron alloy containing more than twenty-five percent nickel to a temperature above that at which it becomes malleable, and progressively reducing the crosssect-ional dimensions of the piece until it reaches a temperature at which the material ceases to be malleable.

7. A method of preparing brittle magnetic materials, which consists in heating an alloy to a temperature of approximately 1325 (1., working the alloy containing approximately eighty percent nickel and twenty percent iron at a temperature above that at which it ceases to be malleable, to produce a fine crystalline structure.

In witness whereof, we hereunto subscribe our names this 20 day of October, A. D., 1927. CHARLES PHILIP BEATH.

HERBERT MARTIN EDWARD HEINICKE. 

